|Publication number||US5974211 A|
|Application number||US 09/019,774|
|Publication date||26 Oct 1999|
|Filing date||6 Feb 1998|
|Priority date||7 Feb 1997|
|Publication number||019774, 09019774, US 5974211 A, US 5974211A, US-A-5974211, US5974211 A, US5974211A|
|Inventors||Joseph B. Slater|
|Original Assignee||Kaiser Optical Systems|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (2), Non-Patent Citations (2), Referenced by (49), Classifications (8), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application claims priority of U.S. provisional application Ser. No. 60/037,691, filed Feb. 7, 1997, the entire contents of which are incorporated herein by reference.
The present invention relates generally to remote optical measurement probes of the type wherein optical fibers are used to stimulate and collect optical spectra for Raman, fluorescence or other forms of detection and, in particular, to such a probe wherein one or more optical elements are used between the remote ends of the fibers and the sample under investigation to enhance collection efficiency.
Fiber-optic probes make it possible to collect optical information such as Raman spectra without having to place the material being characterized inside a spectrometer housing. Such probes therefore simplify the interfacing of spectroscopic systems to chemical processes, and allow analytical instruments to be located remotely from environments in need of spectroscopic monitoring.
The first remote fiber optic probes for Raman spectroscopy were reported by the McCreery group in the early 1980's. Their design used a single optical fiber to deliver laser light to the sample and a single optical fiber to collect light scattered by the sample. More specifically, divergent laser light from the laser delivery fiber was used to illuminate the sample, and light scattered from the sample within the acceptance cone of the collection fiber was transmitted back to the spectrograph. The efficiency of exciting and collecting Raman photons from any individual point in the sample was poor, but the integrated Raman intensity over the unusually large analysis volume compared favorably with the more traditional imaged illumination and collection configurations.
McCreery's dual-fiber Raman probe offered important benefits for remote and routine spectroscopy: 1) the sample could be distant from the Raman instrument, 2) no sample alignment was necessary once the probe was aligned to the spectrograph, 3) the probe could be less 1 mm in diameter, making Raman measurements possible for samples with limited accessibility, 4) the probe could be placed directly in hostile samples (corrosive, hot, etc.) since only silica and the encapsulation material were exposed, and 5) multiple measurements could be made simultaneously by placing multiple collection fibers along the slit height of the spectrograph.
Several improvements to the McCreery Raman probe have more recently been reported. Instead of using just one collection fiber, multiple fibers have been used to increase the collection efficiency, as shown in FIG. 1A. For example, 6 fibers, each having the same diameter as the excitation fiber, may be grouped around the excitation fiber to form a single circular layer, as shown in U.S. Pat. No. 4,573,761. Eighteen fibers, each having the same diameter as the excitation fiber, may also be grouped around the excitation fiber as two circular layers, and so on, though successive layers tend to be less effective at collecting Raman photons than the first layer.
The performance of the McCreery type probe can also be modified for improved collection efficiency and/or working distance by changing the overlap between the emission cone of the excitation fiber and the collection cones of the collection fibers. An early realization of this idea, as disclosed in U.S. Pat. No. 4,573,761, angled the collection fibers such that their optic axes intersected the optic axis of the illumination fiber, as shown in FIG. 1B. This increased the overlap of the excitation and collection cones close to the tip of the fiber probe, where the excitation and collection of Raman photons was most efficient.
The same concept was later implemented in a different way by O'Rourke and Livingston, who ground the tip of the probe into a cone shape, as discussed in U.S. Pat. No. 5,402,508, and illustrated in FIG. 1C. This shape was equivalent to putting prisms (or more correctly, axicon sections) on the collection fibers so that the optic axes of the collection cones crossed the optic axis of the excitation fiber.
One further variation of the McCreery probe design is to use collection fibers having a different diameter than the excitation fiber. This additional variable is useful for changing the working distance of the probe and the fiber coupling to the spectrograph.
One disadvantage of the various arrangements described thus far is that the sample must be very close to the probe tip to realize any significant collection efficiency.
This invention enhances the flexibility and efficiency of fiber-optic probes through the use of imaging optics and other elements positioned between the remote ends of the fibers and the sample under investigation. Such a configuration not only increases the working distance between the fibers and the sample, but also functions to increase the level of overlap between the excitation and collection paths on or (in the case of a transparent sample) within the sample.
In the preferred embodiment, a plurality of collection fibers is disposed circumferentially around a central excitation fiber, enabling a conventional focussing lens arrangement to be used for imaging purposes. The assembly may optionally include a rotationally symmetric diffraction grating disposed between the distal end of the excitation fiber and the lens element(s), causing the excitation energy to assume the shape of an annulus superimposed over the circular image of the collection fibers.
In an alternative embodiment, the excitation and collection fibers are physically spaced apart from one another, facilitating the use of one or more optical elements in either or both of the excitation and collection paths to enhance overall performance. For example, one or more beam-redirecting elements may be used relative to the excitation or collection paths, or both, to further enhance the overlap therebetween. Filtering elements may also be disposed in either or both of the excitation and collection paths to pass or reject the excitation radiation, respectively.
A method of obtaining emission spectra according to the invention includes the steps of directing excitation radiation onto a sample through an excitation optical fiber having a remote end, collecting optical spectra emitted by the sample through a collection fiber having a remote end, and imaging the remote ends of the excitation and collection fibers into a region of overlap on or in the sample. The disclosed apparatus and method may be applied to various fields of stimulated emission, including Raman and fluorescence detection.
FIG. 1A is a drawing of prior-art fiber-optic probe using a single excitation fiber in the plurality of collection fibers;
FIG. 1B illustrates how the configuration of FIG. 1A may be improved by orienting the collection fibers to view a greater percentage of the excitation region;
FIG. 1C is a drawing which shows how the distal tips of the excitation and collection fibers may be modified to enhance the overlap between excitation and collection;
FIG. 2A is a simplified drawing used to illustrate how an optical element may be disposed between the distal tips of the fibers and a sample under investigation to enhance collection efficiency;
FIG. 2B is a drawing in partial cross-section of a physical implementation of the arrangement introduced with respect to FIG. 2A;
FIG. 3 is a drawing of an alternative embodiment of the invention wherein the use of an optical grating is used in conjunction with an imaging element to further enhance the overlap of excitation and collection regions;
FIG. 4 also uses a grating, but in this case, the contrast to that of FIG. 3, the excitation fiber is laterally separate from a plurality of close-packed collection fibers; and
FIG. 5 illustrates yet a further embodiment of the invention utilizing a bandpass and/or a notch filter to enhance the delivery and filtering of the excitation wavelength.
This invention enhances the flexibility and efficiency of remote measurement probes of the type wherein one or more optical fibers are used to excite a sample and one or more optical fibers are used to collect characteristic spectra therefrom. Accordingly, the invention finds use in various fields of stimulated emission, including Raman and fluorescence detection. Typically in such arrangements the excitation fiber includes a proximal end to receive excitation radiation form a source such as a laser and a distal end to deliver the energy to the sample. The collection fiber(s) each include a distal end to gather the spectra emitted by the sample and a proximal end feeding appropriate analytical instrumentation.
Broadly, the invention solves problems associated with existing fiber-optic remote measurement probes by imaging points on, or within, a sample onto the distal end of the probe. Such an arrangement offers several advantages relative to the prior-art design depicted in FIG. 1A. First, whereas the overlap region 110 of the excitation and collection paths in the existing design is necessarily very close to the distal tip 112 of the associated fibers, the use of an optical element 202 affords a significantly greater working distance; for example, from distal end 200 to points 204 within sample 206, as shown in FIG. 2A.
The working distance may be varied through the optical arrangement, thereby providing significant flexibility in terms of physical construction. With the sampling region displaced from the distal end of the probe, the optical elements may sealed in an environment which does not make contact with the sample, thereby protecting probe components from contamination. An additional benefit is that elements used to optically modify (e.g., filters) and/or switch (e.g., shutters) can be inserted between the distal tip of the probe and the sample for enhanced system flexibility.
The invention not only allows for adjustments in terms of working distance, but enhances efficiency by multiplying the overlap of the excitation and collection paths, as better understood with reference to FIG. 2B, which illustrates a physical implementation of the design of FIG. 2A. In this case, a bundle of fibers 220 having an excitation fiber 222 disposed centrally therein is held in a fixture 224 having a distal end including a lens assembly 226, which images the ends of the fibers at a focal plane 228. Although lens assembly 226 shows a pair of opposed plano-convex lenses, other arrangements may be used depending upon the type of imaging desired. A protective transparent window 230 may be used to seal off the lens assembly 226 from the external measurement environment.
Note in FIG. 2B that by virtue of the invention, two overlap regions 240 and 242 are created on either side of a focal plane 228, thereby multiplying the amount of overlap of the excitation and collection beams, thereby enhancing efficiency. Such an arrangement is in contrast to the non-imaged version of a typical fiber-probe, as shown in FIGS. 1A-1C. Using FIG. 1A as an example, since the cone 114 associated with the excitation fiber and the cones 116 and 118 of the collection fibers are all divergent with respect to the distal tip 112 of the probe, the single region of overlap 110 is inconveniently close to the tip 112.
An alternative implementation of the invention is depicted in FIG. 3. Light from the excitation fiber 320 is redirected by a radial (i.e., rotationally symmetric) diffraction grating 322, causing the light to be imaged by the lens into an annular distribution that is superimposed over an annular region containing the set of images of the collection fibers. Note that a conventional axicon could also be used in place of the radial diffraction grating. The redirected light is then brought to a focus superimposed over the image of the collection fibers. In the preferred arrangement grating 322 is supported sufficiently close to the end of the excitation fiber to fill the excitation cone without also overlapping the collection cones of the collection fibers.
Yet a further alternative arrangement is depicted in FIG. 4, wherein the excitation fiber is physically separate from the collection bundle. This makes the task of modifying the direction of excitation light easier in some cases, allowing the use of more standard gratings, lenses, prisms, and so forth to overlap the excitation and collection regions on the sample. Additional flexibility may be gained by placing collimating lenses in front of the collection excitation fibers as well.
As shown in FIG. 5, filters such as bandpass filter 510 and notch filter 520 may be inserted into the excitation path. The function of the notch filter is to reject Rayleigh scattering (non-wavelength-shifted light). If gratings are used for redirection purposes, they may double in function as bandpass elements, thus removing silica Raman contamination. As an alternative to discrete filter elements, the excitation and/or collection fibers may themselves be modified to perform internal filtering functions, as taught in U.S. application Ser. No. 08/803,012, now U.S. Pat. No. 5,862,273 the entire contents of which are incorporated herein by reference.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US4573761 *||14 Sep 1983||4 Mar 1986||The Dow Chemical Company||Fiber-optic probe for sensitive Raman analysis|
|US5402508 *||4 May 1993||28 Mar 1995||The United States Of America As Represented By The United States Department Of Energy||Fiber optic probe having fibers with endfaces formed for improved coupling efficiency and method using same|
|1||*||B. Marquardt, S. Goode, S. Angel, In Situ Determination of Lead in Paint Laser Induced Breakdown Spectroscopy Using a Fiber Optic Probe, Anal. Chem. 1996, 68, pp. 977 981.|
|2||B. Marquardt, S. Goode, S. Angel, In Situ Determination of Lead in Paint Laser-Induced Breakdown Spectroscopy Using a Fiber-Optic Probe, Anal. Chem. 1996, 68, pp. 977-981.|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US6166804 *||20 Sep 1999||26 Dec 2000||General Electric Company||Method and apparatus for obtaining fluorescence data|
|US6598428||11 Sep 2000||29 Jul 2003||Schott Fiber Optics, Inc.||Multi-component all glass photonic band-gap fiber|
|US6603545 *||31 May 2001||5 Aug 2003||Kaiser Optical Systems||Optical measurement probe with leak minimization features suited to process control applications|
|US6831739||24 Jan 2003||14 Dec 2004||Kaiser Optical Systems||Compression-bonded probe window|
|US7019296||24 Oct 2005||28 Mar 2006||Chemimage Corporation||Near infrared chemical imaging microscope|
|US7045757||4 Apr 2005||16 May 2006||Chemimage Corporation||Apparatus and method for chemical imaging of a biological sample|
|US7060955||31 Jan 2005||13 Jun 2006||Chemimage Corporation||Apparatus and method for defining illumination parameters of a sample|
|US7061606||5 Feb 2004||13 Jun 2006||Chem Image Corporation||Near infrared chemical imaging microscope|
|US7068357||24 Oct 2005||27 Jun 2006||Chemimage Corporation||Near infrared chemical imaging microscope|
|US7123360||24 Oct 2005||17 Oct 2006||Chemimage Corporation||Near infrared chemical imaging microscope|
|US7158225||23 Jan 2004||2 Jan 2007||Kaiser Optical Systems||Multi-channel, self-calibrating fiber-coupled raman spectrometers including diagnostic and safety features|
|US7218822||4 Oct 2004||15 May 2007||Chemimage Corporation||Method and apparatus for fiberscope|
|US7221824 *||20 Dec 2002||22 May 2007||Mauna Kea Technologies||Miniaturized focusing optical head in particular for endoscope|
|US7239782 *||3 Sep 2004||3 Jul 2007||Chemimage Corporation||Chemical imaging fiberscope|
|US7268330||13 Jun 2006||11 Sep 2007||Chemimage Corporation||Apparatus and method for defining illumination parameters of a sample|
|US7268861||2 Mar 2006||11 Sep 2007||Chemimage Corporation||Near infrared chemical imaging microscope|
|US7268862||2 Mar 2006||11 Sep 2007||Chem Image Corporation||Near infrared chemical imaging microscope|
|US7283241||31 Jan 2005||16 Oct 2007||Chemimage Corp.||Method and apparatus for a microscope image selector|
|US7317516||2 Mar 2006||8 Jan 2008||Chemimage Corporation||Near infrared chemical imaging microscope|
|US7342214||15 May 2006||11 Mar 2008||Chemimage Corporation||Apparatus and method for chemical imaging of a biological sample|
|US7414725||26 Sep 2007||19 Aug 2008||Chemimage Corporation||Method and apparatus for a microscope image selector|
|US7436500||24 Oct 2005||14 Oct 2008||Chemimage Corporation||Near infrared chemical imaging microscope|
|US7465911||15 Oct 2007||16 Dec 2008||Chemimage Corporation||Apparatus and method for chemical imaging of a biological sample with at least two spectral images of the sample obtained simultaneously|
|US7522797||14 May 2007||21 Apr 2009||Chemimage Corporation||Method and apparatus for fiberscope|
|US7551821||4 May 2007||23 Jun 2009||Chemimage Corporation||Chemical imaging fiberscope|
|US7647092||21 Jun 2002||12 Jan 2010||Massachusetts Institute Of Technology||Systems and methods for spectroscopy of biological tissue|
|US7742564||24 Jan 2007||22 Jun 2010||The University Of North Carolina At Chapel Hill||Systems and methods for detecting an image of an object by use of an X-ray beam having a polychromatic distribution|
|US7773217||17 Feb 2006||10 Aug 2010||Axsun Technologies, Inc.||Probe for tunable laser Raman spectroscopy system|
|US7956991||17 Sep 2008||7 Jun 2011||Chemimage Corporation||Method and apparatus for interactive hyperspectral image subtraction|
|US7990532||5 Mar 2010||2 Aug 2011||Chemimage Corporation||Method and apparatus for multimodal detection|
|US8204174||19 Feb 2010||19 Jun 2012||Nextray, Inc.||Systems and methods for detecting an image of an object by use of X-ray beams generated by multiple small area sources and by use of facing sides of adjacent monochromator crystals|
|US8315358||3 Jun 2010||20 Nov 2012||Nextray, Inc.||Strain matching of crystals and horizontally-spaced monochromator and analyzer crystal arrays in diffraction enhanced imaging systems and related methods|
|US8971488||1 Dec 2009||3 Mar 2015||The University Of North Carolina At Chapel Hill||Systems and methods for detecting an image of an object using multi-beam imaging from an X-ray beam having a polychromatic distribution|
|US20040073120 *||4 Apr 2003||15 Apr 2004||Massachusetts Institute Of Technology||Systems and methods for spectroscopy of biological tissue|
|US20040159789 *||5 Feb 2004||19 Aug 2004||Treado Patrick J.||Near infrared chemical imaging microscope|
|US20050157981 *||20 Dec 2002||21 Jul 2005||Mauna Kea Technologies||Miniaturized focusing optical head in particular for endoscope|
|US20050162646 *||23 Jan 2004||28 Jul 2005||Tedesco James M.||Multi-channel, self-calibrating fiber-coupled raman spectrometers including diagnostic and safety features|
|US20060051036 *||4 Oct 2004||9 Mar 2006||Treado Patrick J||Method and apparatus for fiberscope|
|US20060151702 *||2 Mar 2006||13 Jul 2006||Chemimagie Corporation||Near infrared chemical imaging microscope|
|US20060157652 *||2 Mar 2006||20 Jul 2006||Chemimage Corporation||Near infrared chemical imaging microscope|
|US20060164640 *||2 Mar 2006||27 Jul 2006||Chem Image Corporation||Near infrared chemical imaging microscope|
|US20060170916 *||31 Jan 2005||3 Aug 2006||Voigt Thomas C||Method and apparatus for variable-field illumination|
|US20060170922 *||31 Jan 2005||3 Aug 2006||Xinghua Wang||Method and apparatus for a microscope image selector|
|US20060192956 *||24 Oct 2005||31 Aug 2006||Chemimage Corp||Near infrared chemical imaging microscope|
|US20060221335 *||4 Apr 2005||5 Oct 2006||Bangalore Arjun S||Method and apparatus for interactive hyperspectral image subtraction|
|US20060274301 *||15 May 2006||7 Dec 2006||Chemimage Corporation||Apparatus and method for chemical imaging of a biological sample|
|US20070007444 *||13 Jun 2006||11 Jan 2007||Chemimage Corporation||Apparatus and method for defining illumination parameters of a sample|
|USRE39977||11 Apr 2005||1 Jan 2008||Chemimage Corporation||Near infrared chemical imaging microscope|
|WO2014121389A1 *||5 Feb 2014||14 Aug 2014||Rafal Pawluczyk||Fibre optic probe for remote spectroscopy|
|U.S. Classification||385/33, 385/115, 385/119, 385/37, 385/42|
|6 Feb 1998||AS||Assignment|
Owner name: KAISER OPTICAL SYSTEMS CORP., MICHIGAN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:SLATER, JOSEPH B.;REEL/FRAME:008982/0192
Effective date: 19980205
|3 Mar 2003||FPAY||Fee payment|
Year of fee payment: 4
|15 Mar 2007||FPAY||Fee payment|
Year of fee payment: 8
|4 Apr 2011||FPAY||Fee payment|
Year of fee payment: 12